This invention relates to a cooling liquid temperature control system for an internal combustion engine of the liquid cooled type.
A cooling liquid temperature control system of the prior art for a liquid cooled internal combustion engine will be described by referring to FIG. 1 in which a thermostat valve 3 is mounted at an outlet of a jacket 1 containing a cooling liquid 2 for cooling the engine. When the temperature of the engine rises, the cooling liquid 2 absorbs the heat of the engine and its temperature rises, causing the thermostat valve 3 to move to a lower position to open a radiator inlet passage 4 and close a bypass 5. The cooling liquid of elevated temperature flows through the inlet passage 4 into a radiator 6 where the heat is dissipated. After having its temperature reduced, the cooling liquid 2 flows through a radiator outlet passage 7 into a pump 8 which returns the cooling liquid to the jacket 1 through a return passage 9.
When the temperature of the engine is low, the temperature of the cooling liquid 2 in the jacket 1 does not rise and the thermostat valve 3 does not move to the lower position, so that the radiator inlet passage 4 remains closed and the bypass 5 remains open. Thus the cooling liquid 2 is drawn through the bypass 5 into the pump 8 which returns the cooling liquid 2 to the jacket 1 through the return passage 9.
The opening and closing of the radiator inlet passage 4 by vertical moving of the thermostat valve 3 is decided by a variation in the temperature of the cooling liquid 2. When the temperature of the cooling liquid 2 reaches a predetermined temperature level T1 shown in FIG. 2, in which the abscissa represents the cooling liquid temperature and the ordinate indicates the valve lift, the thermostat valve 3 is moved for opening. In FIG. 2 T1 shows the valve opening temperature and T2 shows the valve closing temperature.
(1) When the predetermined temperature T1 is set at a high level, fresh intake is overheated by the heat of the cylinder and crankcase in a liquid cooled internal combustion engine, particularly in a two cycle engine of the crank chamber pre-pressurizing type, and the temperature of the heated fresh intake is mainly determined by the temperature of the cooling liquid 2, as can be seen in the diagram shown in FIG. 3. Thus when the temperature at which the thermostat is set for operation is high, the air-fuel ratio and charging efficiency of the fuel-air mixture become lower and the power developed by the engines is lower than when the temperature at which the thermostat is set for operation is low, because the volume and flowrate of the intake remain constant.
(2) When the temperature T1 is low, the fresh intake is free from overheating by the heat of the cylinder and crankcase. However, the low temperature of the fresh intake adversely affects vaporization of the fuel-air mixture, causing a reduction in combustion efficiency. The result of this is that fuel consumption increases and the response of power to acceleration decreases. This tendency is particularly marked at partial load of low and intermediate speed and idling, and induces irregular combustion in a two cycle engine.
The application of this cooling liquid temperature control system in an automotive vehicle, snowmobile and a motorcycle would suffer the following disadvantages.
(1) When the temperature T1 is high, the charging efficiency and combustion efficiency of the fuel would drop and the ability to accelerate and to travel upgrade would be reduced.
(2) When the temperature T1 is low, the fuel-air mixture would be difficultly vaporized and the combustion efficiency of the fuel would drop.
At the same time, accelerating ability (acceleration response) would be reduced and fuel consumption during both travelling and idling would increase.